Cláudio> So the question is: what are hard drive makers guaranteeing (ifCláudio> anything at all)?

No guarantees. Nothing that you can get in writing, anyway.

Cláudio> Was a 512B sector write really atomic?

Sometimes.

Cláudio> Is a 4k one?

Sometimes, maybe.

The problem with 4KB physical blocks is that if you do a partial ormisaligned write you'll end up having to do read-modify-write. And thatintroduces are scenario where a subsequent write error will affectlogical blocks that were not part of the I/O request.

However, you also have that with regular drives because they often writemore than the actual block undergoing I/O. For instance to reducehotspot bleed to adjacent sectors.

There have been several unsuccessful attempts at nudging the drivevendors into giving us real guarantees (supercapacitors, NVRAM orflash-backed write cache). No luck so far. So people that care usearrays with non-volatile caches.